General Genetics

1. General Genetics Ayesha M. Khan Spring 2013 Lecture 2

2. Prehistory • The world’s first agriculture is thought to have developed in the Middle East, in what is now Turkey, Iraq, Iran, Syria, Jordan, and Israel, where domesticated plants and animals were major dietary components of many populations by 10,000 years ago. • The first domesticated organisms included wheat, peas, lentils, barley, dogs, goats, and sheep. Selective breeding produced woollier and more manageable goats and sheep and seeds of cereal plants that were larger and easier to harvest. • By 4000 years ago, sophisticated genetic techniques were already in use in the Middle East. Other crops and domesticated animals were developed by cultures in Asia, Africa, and the Americas in the same period.

3. Early written records Early written record • Hindus, Jews sacred writings • Greeks: concept of pangenesis although incorrect but persisted till late 1800’s. • Pangenesis led the ancient Greeks to propose the notion of the inheritance of acquired characteristics.

4. Pangenesis vs Modern Germ-plasm theory

5. Early written records • Aristotle : Greek philosopher (384 – 322 B.C.) • Rejected both pangenesis and the inheritance of acquired characteristics, pointing out that people sometimes resemble past ancestors more than their parents and that acquired characteristics such as mutilated body parts are not passed on. Aristotle believed that both males and females made contributions to the offspring.

6. Modern Genetics • Robert Hooke’s discovery of cells (1665) • Preformationism: inside the egg or sperm existed a tiny miniature adult, a homunculus, which simply enlarged during development. • all traits would be inherited from only one parent—from the father if the homunculus was in the sperm or from the mother if it was in the egg. • Blending inheritance: Offspring are a blend of parental traits (similar to blending of paints).

7. Modern Genetics (contd) • Nehemiah Grew (1641–1712) and GottleibKölreuter (1733–1806) • both botanists studied pollen and carried out numerous crosses. • Gregor Mendel (1822–1884) discovered the basic principles of heredity. Mendel’s conclusions, which were unappreciated for 45 years, laid the foundation for our modern understanding of heredity, and he is generally recognized today as the father of genetics.

8. Mendel first discovered the principles of heredity by crossing different varieties of pea plants and analyzing the pattern of transmission of traits in subsequent generations.

9. Modern Genetics (contd) • Developments in Cytology (1800s): Cell theory: all life is composed of cells, cells arise only from preexisting cells, and the cell is the fundamental unit of structure and function in living organisms. Biologists began to examine cells to see how traits were transmitted in the course of cell division.

10. Modern Genetics (contd) Charles Darwin (1809–1882): -First “Ethologist” –biologists who studied animal behavior from evolutionary perspective • the theory of evolution through natural selection • Darwin recognized that heredity was fundamental to evolution, and he conducted extensive genetic crosses with pigeons and other organisms. • However, he never understood the nature of inheritance, and this lack of understanding was a major omission in his theory of evolution.

11. Modern Genetics (contd) • August Weismann (1834–1914) finally laid to rest the notion of the inheritance of acquired characteristics. He proposed the germ-plasm theory, which holds that the cells in the reproductive organs carry a complete set of genetic information that is passed to the gametes.